This invention relates generally to adhesive coatings, and more specifically to aqueous or waterborne adhesion coatings, and methods of making and using the same.
The demand for olefinic resins, e.g. polyethylene (PE) and polypropylene (PP), in the automotive industry is increasing. In 1998, the automotive industry used 274 million pounds of olefinic resins to coat plastic substrates. By 2005, the automotive industry is projected to use an estimated 750 million pounds of olefinic resins per year.
Thermoplastic olefins (TPOs), mixtures of polypropylene (PP), ethylene-propylene-diene (EPDM), rubber and talc, are fast replacing steel components such as grills, lamp hole covers, automotive bumpers and side body panels. TPO components are less expensive, softer, less dense, easier to mold, easier to recycle and resist corrosion better than their steel counterparts.
TPO poses a significant problem. TPO does not easily adhere to standard one-component (1K) or two-component (2K) coatings. The polypropylene present in TPO creates a low free energy, non-polar surface which hinders bonding.
In an effort to solve this problem, polyolefinic and other plastic substrates have been coated with coating systems containing organic solvents. This solution is undesirable for two reasons: 1) organic solvents are toxic to the environment (high volatile organic compounds) and 2) organic solvents are expensive for waste treatment.
Using an adhesion promoter, namely chlorinated polyolefin (CPO), to bond with the non-polar surface has been proposed, for example in U.S. Pat. No. 4,954,573 (incorporated by reference). Several processes have been proposed to eliminate or minimize the application of CPO adhesion promoters to reduce volatile organic compounds (VOCs) associated with the process and the overall production costs.
U.S. Pat. No. 5,693,423, incorporated by reference, discloses a waterborne coating containing TPO which uses a CPO resin, an ethylene glycol, a surfactant, and an aliphatic amine.
U.S. Pat. No. 4,981,730, incorporated by reference, discloses a low VOC (about 3.5 pounds/gallon) aqueous composition which is suitable as a primer coating on a non-porous substrate such as plastic.
The following United States patents, which are incorporated by reference herein, relate more generally to coating compositions for plastic substrates, including polyolefin substrates: U.S. Pat. Nos. 5,198,485; 5,258,444; 5,288,780; 5,300,363; 5,425,926; 5,427,856; 5,709,946; and 5,777,022.